GB2178499A

GB2178499A - Brake system with both braking and traction slip control

Info

Publication number: GB2178499A
Application number: GB08618019A
Authority: GB
Inventors: Dr Wolfram Seibert; Norbert Ocvirk
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1985-07-30
Filing date: 1986-07-23
Publication date: 1987-02-11
Also published as: DE3527190A1; US4750788A; FR2585652A1; GB2178499B; GB8618019D0; FR2585652B1; JPS6331855A

Description

1 GB2178499A 1

SPECIFICATION

Brake system with slip control This invention relates to a brake system, in tended for automotive vehicles, the brake sys tem having brake slip and traction slip control, and being equipped with a power-assisted brake pressure generating assembly with which wheel brakes are connected through hy draulic fluid lines and with an auxiliary hydrau lic pressure supply system comprising a hy draulic pump, an auxiliary pressure modulation valve controllable by the brake pressure gener ated in the brake pressure generating as- 80 sembly, and a pressure balancing tank. In ad dition, valve arrangements are provided which are inserted, following the brake pressure gen erating assembly, in the hydraulic fluid lines leading to the wheel brakes and which are switched to free passage in their normal posi tion and upon switching into a second switch ing position, link the auxiliary pressure supply system, in lieu of the brake pressure generat ing assembly, hydraulically to the wheel brakes. The brake system is, furthermore, fur nished with wheel sensors and with electronic switching circuits for detection and monitoring of the rotational behaviour of the vehicle's wheels and for the generation of electric brake pressure control signals by means of which brake pressure modulators actuatable electro magnetically are controllable for the purpose of slip control.

In our co-pending GB Application No. 100 8600344 a brake system of this kind is de scribed which in one embodiment is corn prised of a master cylinder with preceding va cuum booster. If and when locking of a wheel is imminent, a pressure is built up in the aux- 105 iliary hydraulic pressure supply system whose level is controllable, with the aid of the auxiliary pressure modulation valve, by the pressure existing in the working chamber of the master cylinder and being proportional to the 110 pedal force. Said auxiliary pressure leads to the switching of multiway valves which in their normal position connect the working chambers of the master cylinder with the 50 wheel brakes and upon commutation link the 115 wheel brakes to the controlled auxiliary pressure instead of to the master cylinder. The brake pressure modulators controlled by the slip control are inserted in the hydraulic fluid 55 lines between the described multiway valves and the wheel brakes, respectively between the wheel brakes and the balancing tank. It will be appreciated that in this way the brake circuits of that brake system are static in the 60 event of non-controlled braking operations, whereas the brake pressure is supplied dynamically from the auxiliary pressure supply system on the start of the slip control action and upon the commutation of the multiway 65 valves. When the control action starts, the exits of the master cylinder are shut off. It will be safeguarded even in unfavourable conditions, in particular in the event of a strong pressure drop when driving on a slippery road surface as well as in the event of a failure of the auxiliary pressure supply, that sufficient hydraulic fluid remains available anyway in the master cylinder and, consequently, in the brake circuit. 75 The system according to the aforementioned application is distinguished by the particularly unsophisticated set-up and by a reliable mode of operation. The present invention has an object of further developing, a brake system of this kind with a minimum of design efforts in such a manner that the brake system is not only suited for the control of the brake slip but also for the control of the traction slip. 85 According to the present invention there is provided a brake system with brake slip and traction slip control, including a power-assisted brake pressure generating assembly with which wheel brakes are connected through hydraulic fluid lines, an auxiliary hydraulic pressure supply system comprising a hydraulic pump, an auxiliary pressure modulation valve and a pressure balancing tank, valve arrangements inserted following said brake pressure generating assembly, in the hydraulic fluid lines leading to the wheel brakes, which valve arrangements are switched to free passage in their normal position and upon switching into a second switching position, link said auxiliary pressure supply system, in lieu of said brake pressure generating assembly, hydraulically to said wheel brakes, and including wheel sensors and electronic switching circuits for detection and monitoring of the rotational behaviour of vehicle wheels and for the generation of electric brake pressure control signals by means of which brake pressure modulatorsJor example pairs of valves, actuatable electromagnetically for the purpose of slip control are controllable, characterized in that a multiway valve which is normally switched to free passage and is switchable to closed passage for the purpose of traction slip control is inserted in an hydraulic fluid line leading from the said hydraulic pump, via the said auxiliary pressure modulation valve, to the said pressure balancing tank, and in that any movement of hydraulic fluid relative to said brake pressure generating assembly is prevented during a traction slip control action and the wheel brakes of driven wheels are hydraulically separated from the wheel brakes of non-driven wheels. Thus the above object can be achieved in a technically advanced manner and with very slight additional design and manufacturing efforts as compared with the unit according to the aforementioned application.

As soon as the electronic system detects the risk of a racing of the wheels, respectively of an excessive traction slip by analyzing the 2 GB2178499A 2 rotational behaviour of the wheels, the hydraulic pump will be switched in automatically and the multiway valve which is inserted in the hydraulic path going from said pump, via the auxiliary pressure modulation valve, to the pressure balancing tank will be switched over to closed passage. Either by the auxiliary pressure or electromagnetically, the wheel brakes will be linked to the auxiliary pressure supply system and the exits of the brake pressure generating assembly will be closed. If the driven as well as the non-driven wheels are linked to a common brake circuit, then the two wheel brakes will moreover be decoupled hydraulically by closing the hydraulic fluid path leading to the nondriven wheel.

According to an advantageous embodiment of the invention, the multiway valve inserted in the hydraulic fluid path going from the delivery side of the pump, via the auxiliary pressure modulation valve, to the pressure balancing tank is arranged between said modulation valve and said pressure balancing tank. The forementioned multiway valve is expediently designed as a 2/2-way valve which is actuatable electromagnetically.

Another embodiment of the invention is such that the valve arrangements inserted following the brake pressure generating as- sembly, in the hydraulic fluid lines leading to the wheel brakes are configured in the form of pressure-controlled multiway valves which are commutatable by the auxiliary pressure and which in their normal position hydraulically connect the brake pressure generating assembly, and upon switching the auxiliary pressure supply system, with the wheel brakes. In this context, the switching may also take place when the auxiliary pressure exceeds a predetermined threshold value.

Alternatively, the valve arrangements inserted in the lines going to the wheel brakes, following the brake pressure generating assembly, may be realized in the form of elec- tromagnetically actuatable multiway valves which in the de-energized condition connect the brake pressure generating assembly, and upon energization of the auxiliary pressure supply system, with the wheel brakes.

Advantageously, the pressure-controlled and 115 the electromagnetically actuatable valve arrangements may both be configured in the form of 3/2way valves.

For the purpose of a safe pressure reduction upon the release of the brake, a non-return valve lockable by pressure is arranged parallel to each of the valve arrangements, each said non-return valve connecting the hydraulic fluid path leading to the related wheel brakes with the brake pressure generating assembly and openable in the direction of the brake pressure generating assembly. It will be expedient if the shutting-off of the said non-return valve is effected by the auxiliary pressure which originates in the event of shutting-off of the mul- 130 tiway valve positioned between the modulation valve and the balancing tank.

In one embodiment of the present invention, it is, furthermore, envisaged to configure the brake pressure generating assembly in the form of a tandem master cylinder with a preceding vacuum booster which is provided with two hydraulically separate brake circuits to which the wheel brakes are connected diagonally, each of the non-driven wheels allowing to be decoupled from the driven wheel of one and the same brake circuit by switching over an electromagnetically actuatable 2/2-way valve which is open in the de-energized condi- tion and through which the non-driven wheel is connected hydraulically.

In lieu of the electromagnetically actuatable valve, a pressurecontrolled 2/2-way valve may, by alternative, be inserted, the pressure coming about, by action of the 2/2-way valve, in the return line from the modulation valve to the pressure balancing tank when the traction slip control action starts being, in this configuration, applied to these valves as a control pressure.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic representation of a brake pressure generating assembly and of the most important components of a embodiment of brake system and of their hydraulic and electric circuitry; and Figure 2 is another embodiment of the in- vention in an identical kind of representation to Figure 1.

In the embodiment illustrated in Figure 1, the brake system comprises a brake pressure generating assembly 1 which is substantially composed of a tandem master cylinder 2 and a vacuum booster 3. The brake is actuated through a pedal 4.

In addition to the external energy required for the vacuum booster 3, which is taken in the known manner from a vacuum source (not shown in the drawing), the brake system is equipped with an auxiliary hydraulic pressure supply system which is needed solely for the slip control. Said auxiliary pressure supply system is comprised of a hydraulic pump 5 which is driven by means of an electric motor M, of an auxiliary pressure modulation valve 6, and of a pressure balancing tank 7 which forms a constructional unit with the supply tank and hydraulic fluid reservoir required for operation of a customary master cylinder.

Furthermore, valve arrangements 8, 9 are provided which are configured in the form of pressure-controlled 3/2-way valves in the em- bodiment illustrated in the drawing. In the initial position or normal position of rest of said valves 8, 9, that is, as long as no control pressure at all or only a control pressure ranging below the point of switching exists in control lines 10, 11, said valves 8, 9 connect the 3 GB2178499A 3 1 1 two brake circuits 1, 11 ofthe tandem master cylinder 2 with inlet valves EV,, EV, by way of which wheel brakes 12, 13 or 14, 15 re spectively of each diagonal are linked to said brake circuits 1, 11, respectively. In each of the hydraulic fluid lines leading to non-driven rear wheels HL, HR, a 2/2-way valve 16, 17 is inserted which is switched to free (open) pas sage in the normal position.

Upon switching of the valve arrangements 8, 9, instead of the master cylinder 2, that is to say, instead of the brake circuits 1, 11, an auxiliary pressure supply line 18 will be opened up toward the wheel brakes 12 to 15 through the inlet valves EV,, EV,. In this switching position, viz. in the second switch ing position of the valve arrangement 8, 9, any removal of hydraulic fluid from the work ing chambers 19, 20 will be rendered impos sible, as a result whereof any further slide of the master cylinder pistons 21, 22 to the left and any drainage of the working chambers 18, 19 will be prevented.

A 2/2-way valve 23 switched to free (open) passage in the normal position establishes a connection from the auxiliary pressure supply line 18 to the pressure balancing tank or res ervoir 7, as a result whereof a reduction of the auxiliary pressure is safeguarded on the end of a control action and on switching back 95 of that valve into the position illustrated. A reduction of the pressure via the pump is not possible because of a non-return valve 24 by way of which the pressure side of the pump 5 is linked to the supply line 18. The suction 100 side of the pump, too, is linked to the joint pressure balancing tank or reservoir 7.

The auxiliary pressure modulation valve 6 contains a control chamber 25 which is con nected, by way of a hydraulic fluid line 26, to 105 one of the two working chambers of the mas ter cylinder 2, namely to the working chamber 19 in the case illustrated in the drawing. The pressure existing in the control chamber 25 is transmitted, through a piston 27, to a ball seat valve 28 which throttles the flow of hy draulic fluid from the pump 5, through the non-return valve 24, connecting line 18', through a chamber 29 inside the modulation valve 6 and through a return line 30, to the 115 balancing tank or reservoir 7 proportionally to the control pressure. When the brake is not actuated and the working chamber 19 is un pressurised, the ball seat valve 28 is as good as open because a spring 31 inside the con- 120 trol chamber 25 defines the position of the piston 27 solely in the unpressurised condition and exerts only a slight closing force on the ball seat valve 28.

Furthermore, a 2/2-way valve 32 which is normally switched to free (open) passage and is switchable into a shut-off position and which is inserted in the return line 30 con necting the chamber 29 of the modulation valve 6 with the balancing tank or reservoir 7 130 is of importance for the brake system according to the present invention. This check valve 32 is necessary in order to be able to bring about an auxiliary hydraulic pressure for trac- tion slip control in the supply line 18, 18' when the brake is not actuated, the control chamber 25 is then unpressurised and, consequently, the ball seat valve 28 is open.

Certain defects of the brake system can be signalled with the aid of a pressure comparatorswitch (DI?WS) 33 in conjunction with a warning device (not shown in the drawing).

For the monitoring of the rotational behaviour and for the detection of an imminent locking or of a racing tendency, the vehicle wheels are equipped with inductive sensors S,, S,, S,, S, which furnish information in the form of electric signals to an electronic switching circuit 34 supplying, upon recogni- tion, logical operation and signal processing, control signals for the individual electromagnetically actuatable valves through its output lines a,, to a.. Through the connection a., the electric drive motor M of the hydraulic pump 5 will be switched on as soon as auxiliary hydraulic pressure is required for the purpose of slip control. In the illustrated embodiment of the invention, the inlet valves EV,, EV,, the outlet valves AV,, AV, needed for the pressure reduction, the valve 23 safeguarding the pressure balance, and, finally, the valves 16, 17 and 32 which are necessary for a traction slip control are actuated electromagnetically.

The brake system according to Figure 1 operates as follows:

As long as neither a brake slip nor a traction slip control action is required, all valves except for the valves inside the master cylinder 2 remain in the position illustrated. The hydraulic pump remains out of functioning. The system works like a conventional master cylinder with an integrated vacuum booster.

The brake slip control action will start as soon as a wheel threatens to lock during a braking operation. For this purpose, the driving motor M will be switched in through the switching circuit 34. The chamber 25 of the modulation valve 6 will be already under pressure at this moment. An auxiliary pressure proportional to the pedal force will develop in the auxiliary pressure supply line 18 and will lead to the switching of the valve arrangements 8 and 9 in the manner described in the foregoing, as a result whereof the auxiliary pressure supply system instead of the master cylinder 2 will be connected to the wheel brakes 12 to 15. Maintenance of the pressure at a constant level and a pressure reduction in the course of a brake pressure control proce- dure will now be subject to the control with the aid of the pairs of inlet and outlet valves EV,, AV,; EV,, AV, which receive electric control signals through the output lines of the switching circuit 34.

If and when, however, with the brake not 4 GB2178499A 4 being operated or independent of the oper- ation of the brake, a traction slip control action becomes necessary which, too, will be noticeable, with the aid of the electronic switching circuit 34, from the rotational behaviour of the individual wheels and from the relevant sensor signals, then auxiliary hydraulic pressure will be generated again in that the drive motor M of the pump 5 is put into running by means of a signal at the output line a. and the multiway valve 32 in the return line 30 is switched over electromagnetically. Also in this case, the pressure-controlled valve arrangements 8 and 9 will connect the auxiliary pressure supply line 18, instead of the brake circuits 1, 11, with the hydraulic fluid lines 1', 11' leading to the wheel brakes. In this instance, the hydraulic fluid path to the nondriven wheels HL, HR will be interrupted by energization and cummutation of the valves 16, 17, so that only the wheel brakes 12, 14 will be subject to hydraulic brake pressure in the phase of traction slip control action. The pressure is proportioned and its course predetermined through the pairs of inlet and outlet valves EV,, AV,, EV2, AV,.

The components required for the brake slip control, in particular the auxiliary hydraulic pressure supply system, the pressure-con- trolled valve arrangements and the pairs of inlet and outlet valves, are, thus, utilized also for the traction slip control. Only the two sep arating valves 16, 17, which are disposed in the hydraulic fluid lines leading to the non driven wheels, and the separating valve 32, in 100 the return line 30 between the auxiliary pres sure modulation valve 6 and the balancing tank or reservoir 7, are additionally required.

Accordingly, the extra expenditure required to supplement the system to form a brake slip plus traction slip control system is extremely low.

The pressure-controlled valve arrangements, that is, the 3/2-way valves 8 and 9 may, by alternative, very well be substituted with corresponding valves actuatable electromagnetically. This will bear the advantage that the switching of the valves can be rendered dependent on still other conditions in a very simple manner. Indeed, electric signals are very easily incorporated in logic circuits.

The brake system according to Figure 2 differs in only a few features from the system described above. An explanation of the com- ponents and details coinciding with Figure 1 is, therefore, not made here. Identical components are designated by identical reference numerals in both figures.

According to Figure 2, non-return valves 35, 36 are disposed parallel to the valve arrangements 8, 9, said non-return valves 35, 36 each linking the inlet of the inlet valve EV,, respectively EV21 to the pertaining connection of the brake circuit 1, respectively 11 at the tandem master cylinder 2. The said non-return valves will safeguard a pressure reduction through the master cylinder 2 toward the ba lancing tank or reservoir 7 on release of the brake.

As a special feature, said non-return valves 35, 36 have a control input 37, 38 through which they can be shut off by applying to them a control pressure. Such shutting-off is necessary for the traction slip control, since the brake is not actuated in this phase and, therefore, the master cylinder 2 remains unpressurised.

The control pressure to shut off the nonreturn valves 35, 36 is tapped off from the chamber 29 of the auxiliary pressure modulation valve 6 or from the hydraulic fluid path between said modulation valve and the multiway valve 32 switched over into the shut-off position in the phase of traction slip control action.

In the embodiment of Figure 2, the valves 16 and 17 of Figure 1 can be replaced by 2/2-way valves 40, 41 which are pressurecontrolled valves, rather than electromagneti- cally actuated, by means of which valves the respective non-driven wheel can be decoupled hydraulically from the driven wheel positioned in the same brake circuit. Indeed, pressure will exist at the tap 39 of the control pressure only during the phase of traction slip control action because the connection to the pressure balancing tank or reservoir 7 will be open in the event of normal braking operations and in the event of a brake slip control action.

Claims

1. A brake system with brake slip and traction slip control, including a power-assisted brake pressure generating assembly with which wheel brakes are connected through hydraulic fluid lines, an auxiliary hydraulic pressure supply system comprising a hydraulic pump, an auxiliary pressure modulation valve and a pressure balancing tank, valve arrange- ments inserted following said brake pressure generating assembly, in the hydraulic fluid lines leading to the wheel brakes, which valve arrangements are switched to free passage in their normal position and upon switching into a second switching position, link said auxiliary pressure supply system, in lieu of said brake pressure generating assembly, hydraulically to said wheel brakes, and including wheel sensors and electronic switching circuits for de- tection and monitoring of the rotational behaviour of vehicle wheels and for the generation of electric brake pressure control signals by means of which brake pressure modulators, for example pairs of valves, actuatable electro- magnetically for the purpose of slip control are controllable, characterized in that a multiway valve (32) which is normally switched to free passage and is switchable to closed passage for the purpose of traction slip control is in- serted in an hydraulic fluid line (18', 30) lead- GB 2 178 499A 5 r 45 v ing from the said hydraulic pump (5), via the said auxiliary pressure modulation valve (6), to the said pressure balancing tank (7), and in that any movement of hydraulic fluid relative to said brake pressure generating assembly (1) is prevented during a traction slip control action and the wheel brakes (12, 14) of driven wheels (VR, VIL) are hydraulically separated from the wheel brakes (13 15) of non-driven wheels (HR, HL).

2. A brake system as claimed in claim 1, characterized in that the said multiway valve (32) inserted in the said hydraulic fluid path (18', 30) including the said auxiliary pressure modulation valve (6) is arranged between the said modulation valve (6) and the said pressure balancing tank (7).

3. A brake system as claimed in claim 1 or claim 2, characterized in that the said valve arrangements (8, 9) inserted following the said brake pressure generating assembly (1), in the hydraulic fluid lines leading to the wheel brakes (12-15) are configured in the form of pressure-controlled multiway valves which are switchable by the auxiliary pressure and in their normal position hydraulically connect the said brake pressure generating assembly (1), and upon their commutation the said auxiliary pressure supply system (5, 6, 18), with the wheel brakes (12 to 15).

4. A brake system as claimed in claim 3, characterized in that the switching of the said valve arrangement multiway valves (8, 9) takes place as soon as the auxiliary pressure exceeds a predetermined threshold value.

5. A brake system as claimed in claim 1 or claim 2 characterized in that the said valve arrangements (8, 9) inserted in the hydraulic fluid lines going to the wheel brakes (12 to 15) and following the said brake pressure generating assembly (1) are configured in the form of electromagnetically actuatable multiway valves which in their normal position of rest connect the said brake pressure generating assembly, and upon switching the said auxiliary pressure supply system, with the wheel brakes.

6. A brake system as claimed in any one of claims 3 to 5, characterized in that the said valve arrangement multiway valves (8, 9) are configured in the form of 3/2-way valves.

7. A brake system as claimed in any one of claims 1 to 6, characterized in that a nonreturn valve (35, 36) lockable by pressure is arranged parallel to each of the said valve arrangements (8, 9), each said non-return valve (35, 36) connecting, the hydraulic fluid path leading to the related wheel brakes (12 to 15) with the said brake pressure generating as- sembly (1), and being switchable to free passage in the direction of the said brake pressure generating assembly (1).

8. A brake system as claimed in claim 7, characterized in that the said non-return valve (35, 36) can be shut off by the auxiliary pres- sure which originates in the event of locking of the said hydraulic fluid line (18', 30) leading via the said auxiliary pressure modulation valve (6).

9. A brake system as claimed in any one of claims 1 to 8, characterized in that the said multiway valve (32) inserted in the said hydraulic fluid path (18', 30) leading from the said hydraulic pump (5), through the said aux- iliary pressure modulation valve (6), to the said pressure balancing tank (7) is configured as an electromagnetically actuatable 2/2-way valve which is open in the de-energized condi tion.

10. A brake system as claimed in any one of claims 1 to 9, characterized in that the said brake pressure generating assembly (1) is con figured in the form of a tandem master cylin der (2) with a preceding vacuum booster (3) and is provided with two hydraulically separate brake circuits (1, 1'; 11, ll') to which the said wheel brakes (12 to 15) are connected diagonally, each of the said non-driven wheels (HR, HL) allowing to be decoupled from the driven wheel (VR, VQ of one and the same brake circuit by switching of an electromagnetically actuatable 2/2-way valve (16, 17) which is open in the de-energized condition and through which the said non-driven wheel MR, HL) is connected hydraulically.

11. A brake system as claimed in any one of claims 1 to 9, characterizd in that the said brake pressure' generating assembly is provided with two brake circuits (1, 1'; 11, ll') to each of which one driven and one non-driven wheel (VR, HL; VL, HR) are connected, the said non-driven wheel (HL, HR) being linked by way of a pressure-controlled 2/2-way valve (40, 41) which is open in the normal position and switchable into its shut-off position by the pressure developing when the hydraulic fluid path (30) from the said auxiliary pressure modulation valve (6) to the said pressure balancing tank (7) is closed upon the start of a traction slip control action.

12. A brake system with brake slip and traction slip control substantially as herein described with reference to and as illustrated in Figure 1 or Figure 2 of the accompanying drawings.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1987, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.